Summary: The patterns of absorption and translocation of 14C clopyralid commercially formulated as the acid, monoethanolamine salt, potassium salt, 2‐ethylhexyl ester and 1 ‐decyl ester were compared in Cirsium arvense and Polygonum convolvulus grown under three environmental regimes. Plants were grown under a 35% or 65% RH regime in silica sand maintained at 33% w/w moisture or under a water stress regime at 65% RH. Approxi mately 26,39,86,93 and 100% of the applied 14C‐activity from the 2‐ethylhexyl ester, acid, monoethanolamine salt, 1‐decyl ester and potas sium salt, respectively, were recovered 72 h after application to glass cover slips placed in the growth room. However, loss of applied 14C‐activity after application of the five formulations to both plant species was significant only for the 2‐ethylhexyl ester. Regardless of environmental regime, the acid was the most readily absorbed formulation. In contrast to the acid, the salts and esters were less readily absorbed. When the data were expressed as a percentage of absorbed radioactivity, there was no significant difference in translocation when the acid, monoethanolamine salt and potassium salt were compared. However, significantly smaller quantities of the absorbed 2‐ethylhexyl and 1‐decyl ester were exported from the treated leaf. These results indicate that once absorbed, the esters do not readily partition out of the cuticle, whereas the acid and two salts move into the symplast for subsequent translocation. When the results of the three environmental regimes were compared, the absorption of the monoethanolamine and potas sium salts were greatly reduced under low humi dity or water stress, whereas the acid and esters were not affected.

Experiments were conducted in a controlled environment growth room to compare the phytotoxicity of five formulations of clopyralid and to determine the effect of post-treatment simulated rainfall applications on the efficacy of these formulations. Clopyrahd, formulated as the acid, monoethanolamine salt, potassium salt, 2-ethylhexyl ester or 1-decyl ester was applied to Cirsium arvense or Polygonum convolvulus at the 8-10 and 4-6 leaf stage of development, respectively.Based on the shoot and root dry weight data from both species, the 2-ethylhexyl ester was consistently less phytotoxic than the other four formulations. With respect to Cirsium arvense shoot and root dry weight, there was no difference in efficacy between the acid, monoethanolamine salt, potassium salt and 1-decyl ester. Root dry weight changes of Polygonum convolvulus did not correlate well with an increase in dose of the five formulations. Maximum increase in stem diameter of Polygonum convolvulus occurred after application of 100 g a.e. ha~' of the acid, monoethanolamine salt, potassium salt and 1-decyl ester whereas with the 2-ethylhexyl ester, the maximum increase occurred after application of 200 g a.e. ha"'. Simulated rainfall was applied 3, 6, 9 or 12 h after application of 200 g a.e. ha~' of the five clopyralid formulations to both species. Rainfall reduced the efficacy of clopyralid, regardless of the formulation or species. The 2-ethylhexyl ester was less efficacious than the other four formulations, irrespective of the timing of simulated rainfall. Efftcacite de cinq formulations differentes de clopyralid sur Cirsium arvense (L.) Scop, et Polygonum convolvulus L. Des essais ont et6 conduits dans des chambres de croissance en milieu controle pour comparer la phytotoxicite de cinq formulations de clopyralide et pour determiner l'effet d'une pluie artificielle apres le traitement sur l'efficacitd e ces formulations. Le clopyralid formule comme acide, sel monoethanolamine, sel de potassium, 2-ethylhexyl ester ou 1-decyl ester a et6 applique sur Cirsium arvense ou Polygonum convolvulus aux stades respectifs de 8 a 10 feuilles et de 4 a 6 feuilles. En se basant sur les poids sees des tiges et racines des deux especes, on a vu que le 2-ethylhexyl ester 6tait notamment moins phytotoxique que les 4 autres formulations. En regard des poids sees des tiges et racines de Cirsium arvense, il n'y a pas eu de difference d'efficacite entre l'acide, le sel monoethanolamine, le sel de potassium et 1decyl ester. Les changements du poids sec racinaire chez Polygonum convolvulus n'etaient pas bien correl6s avec une augmentation de la dose des cinq formulations. Le maximum d'augmentation du diamfetre de la tige de Polygonum convolvulus a 6t6 observe apres l'application de 100 g ha~' d'acide, sel monoethanolamine, de sel de potassium et de 1-decyl ester tandis qu'avec le 2-ethylhexyl ester, le maximum a ete observe aprds une application de 300 g ha"'. Des pluies artificielles ont et6 faites 3, 6, 9 ou 12 h aprfes l'application de 200 g ha~' des cinq formulatio...

Summary: A model system consisting of chemically isolated cuticular membranes placed on agar was used to study the penetration of various formulations of 14C‐labelled clopyralid, fluroxypyr, triclopyr, picloram, and 2,4‐D into and through cuticular membranes. Clopyralid, commercially formulated as the acid, or 1‐decyl ester was rapidly absorbed after 12 h by isolated cuticles of Euonymus fortunei. There was less absorption of the monoethanolamine and potassium salt formulations when compared to the acid and 1‐decyl ester. However, in terms of the absorbed 14C‐activity that partitioned into the agar, there was no difference between the acid and salt formulations with approximately 90% being partitioned after 48 h. Conversely, the 1‐decyl ester formulation of clopyralid was retained in the cuticle; less than 5% of the absorbed fraction was recovered in the agar after 48 h. When the acid forms of clopyralid, fluroxypyr, triclopyr, picloram, and 2,4‐D were compared, there was little or no difference in absorption among the herbicides. However, the 14C‐activity from clopyralid partitioned the most (90%) and triclopyr the least (50%) into the agar. When ester formulations of clopyralid, fluroxypyr, and triclopyr were compared, at least 95% of the 14C‐activity was absorbed 24 h after application. However, of the amount absorbed, significantly more of the butoxyethyl ester of triclopyr (36%) partitioned into the agar than did the 1‐decyl ester of clopyralid (6%) or the 1‐methylheptyl ester of fluroxypyr (5%). Differential retention of various herbicide formulations in this model system may explain, in part, the differences in absorption and translocation among radiolabelled clopyralid formulations observed in previous research (Kloppenburg & Hall, 1990).